New hepatitis agents continue to be recognized. Recently, a form of epidemic hepatitis occurring in India was found not to be caused by recognized hepatitis viruses. Attempts to transmit an agent from acute-phase clinical samples to primates are in progress. Attempts to transmit an agent from clinical specimens from these outbreaks have been partially successful. Transient low-level liver enzyme elevations and histopathologic changes consistent with hepatitis in liver biopsies have been observed in some animals, but this has not been uniform, and attempts to serially transmit an agent in chimpanzees and marmosets have also produced irregular results. Characteristic histopathologic changes distinct from those seen in type A hepatitis, type B hepatitis and non-A non-B hepatitis have been reported.